[Telemetry] Refactor class comment in cc files

Bug: None
Change-Id: Ife1946407c01e049b032900f8b25071ab93f5be6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3141449


Reviewed-by: Oleh Lamzin <lamzin@google.com>
Commit-Queue: Oleh Lamzin <lamzin@google.com>
Cr-Commit-Position: refs/heads/main@{#918731}